1. Field of the Invention
A number of devices are available for delivering a drug into the lungs of a patient. Once such device is a nebulizer, which is a device that is used for converting a liquid, such as a liquid medication, into an aerosol which is then inhaled by the patient, typically through a mouthpiece. A number of different types of nebulizers exist, such as, without limitation, jet nebulizers (sometimes referred to as pneumatic nebulizers) and ultrasonic nebulizers. A typical jet nebulizer uses compressed air to generate the aerosol from the liquid. One type of ultrasonic nebulizer employs acoustic waves having an ultrasonic frequency that are directed to a point on the surface of the liquid that is to be converted into an aerosol. At the point on the surface of the liquid where these ultrasonic waves converge, they will produce capillary waves that oscillate at the frequency of the ultrasonic waves. If the amplitude of the waves is large enough, the peaks of the capillary waves will break away from the liquid and be ejected from the surface of the liquid in the form of droplets, thereby forming the aerosol. A device that is often used for generating ultrasonic waves in an ultrasonic nebulizer is a piezoelectric transducer (such as a piezoelectric crystal), which vibrates and generates ultrasonic waves in response to an applied electric field. In another type of ultrasonic nebulizer, the liquid that is to be converted into an aerosol is forced through a mesh (thereby creating liquid droplets) by the vibration of a piezoelectric crystal acting upon a horn. In this type of ultrasonic nebulizer, typically referred to as a mesh nebulizer, the gauge of the mesh determines the size of the droplets which are created to form the aerosol.
2. Description of the Related Art
Conventional nebulizer systems provide a continuous aerosol/drug output, and thus the amount of drug inhaled is dependent upon the patient's breathing pattern. The duty cycle of the patient's breathing pattern is typically 40:60. This means that the patient spends 40 percent of a single respiratory cycle in inspiration and 60 percent of the time in expiration. Thus, 60 percent of the drug delivered from the nebulizer will be wasted to the environment during expiration. In addition, the breathing pattern of a single patient over the course of a treatment will vary.
In order to address these issues, more sophisticated nebulizer systems, referred to as adaptive nebulizer systems based on what is known as Adaptive Aerosol Delivery (AAD) technology, have been developed which adapt the delivery of aerosol to the patient's breathing pattern, delivering medication only when the patient is inhaling through the mouthpiece. Because adaptive nebulizer systems are able to deliver the medication very efficiently (nearly all of the medication supplied to the nebulizer is actually delivered to the patient), it is important that the amount of medication supplied to the nebulizer be as precise as possible so that the patient will receive the correct dose.
In one known method of controlling the volume of medication, a syringe is used to draw a precise amount of medication from a vial, and the drawn medication is then transferred to a chamber in the nebulizer. This method has a number of disadvantages. For example, patients with poor dexterity, such as the elderly, may find it difficult to use a syringe in this manner Also, the use of syringes presents the danger of needle-stick injuries, and sharps containers are required for disposal. Syringes also present an additional part that the patient must keep track of and carry with them when they leave their home.